Rethink Imaging

EP 19 • May 15, 2025

Why Gonadal Shielding in X-rays Actually Increases Radiation Dose

Featured Guest

Dr. Summer Kaplan, MD

Associate Professor of Clinical Radiology, University of Pennsylvania School of Medicine; Pediatric Radiologist • Children's Hospital of Philadelphia

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Gonadal shielding has been standard practice in X-ray since the 1950s, put in place to protect reproductive organs from radiation. Dr. Summer Kaplan set out to test whether it still makes sense. Her 2015 research started with a simple observation: modern X-ray machines use a sensor to decide how much radiation to deliver, and a lead shield placed over that sensor blocks it. When the machine cannot read enough light, it keeps exposing until it hits its threshold. The result is more radiation, not less, which is the opposite of what shielding was meant to do. In this episode she walks through the physics, the history, and why the field is moving away from a practice most people assumed was protective.

Kaplan also unpacks how our understanding of radiation risk has changed. Fifty years of data show the gonads carry roughly 8 percent of whole-body radiation risk, not the quarter once assumed, and there is no evidence of heritable effects in humans. Shielding can also hide findings radiologists need to see. She talks through how to explain the change to anxious families, why staff and parents still wear lead while the patient does not, and where emerging tools like predictive AI could cut dose by helping decide who actually needs imaging. The through-line: keep updating practice as the evidence changes, because the status quo is not the same as best practice.

Host

Chris St. John

Host, Rethink Imaging • Imalogix

Featured Guest

Dr. Summer Kaplan, MD

Associate Professor of Clinical Radiology, University of Pennsylvania School of Medicine; Pediatric Radiologist • Children's Hospital of Philadelphia

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Key Takeaways

Gonadal shielding began in the 1950s when X-ray worked like old film photography, but modern machines use automatic exposure control, and a shield over that sensor forces the machine to keep exposing until it hits its light threshold, raising dose instead of lowering it.
Understanding of risk has changed: the gonads were once weighted at about a quarter of whole-body radiation risk, but current data put it near 8 percent, and 50 years of evidence shows no heritable effects in humans.
Because the gonads are less radiation-sensitive than the colon, stomach, and bone marrow, shielding them can roughly double the dose to more sensitive tissues nearby, and it can block findings radiologists need to see.
The FDA, the American College of Radiology, the American Association of Physicists in Medicine, and the NCRP no longer recommend gonadal shielding, and technologist training programs have stopped teaching it.
Portable X-rays lack automatic exposure control, so shielding there does not raise dose the same way, but those exams are usually done on the sickest patients, where a shield hiding a finding is the bigger risk.

Full Transcript

Rethink Imaging Podcast Transcript

Guest: Summer Kaplan

Host: Chris St. John

SUMMER KAPLAN 00:00:00 The sensor wants to see a certain threshold amount of light or radiation. If you put something in front of that sensor, it doesn’t see that amount of light, so it will actually keep exposing longer until it reaches that threshold. We reasoned that the shields might actually be contributing to higher doses because they could be blocking that sensor in the X-ray machine. So that’s what prompted the research we did—the idea, the theory that gonadal shields sit right in front of the X-ray sensor and could actually be resulting in more radiation rather than less, which is the opposite of the intention of shielding and protecting from radiation.

CHRIS ST. JOHN 00:00:41 Welcome to Frame by Frame: Rethink Imaging, a podcast by Imalogix. Here, we explore the intricate world of medical imaging, aiming to dissect the field and inspire both professionals and curious minds alike. I’m your host, Chris St. John. Today, we are joined by Dr. Summer Kaplan, who is an associate professor of clinical radiology at the University of Pennsylvania School of Medicine and a practicing pediatric radiologist at the Children’s Hospital of Philadelphia. With over a decade of experience in pediatric imaging and a deep focus on quality improvement, she has become a key voice in advancing safer, smarter imaging practices for children. Dr. Kaplan is also the recipient of the prestigious Caffey Award for her research challenging longstanding assumptions about gonadal shielding in radiology, and that’s where we’re going to get started today. Dr. Kaplan, welcome to Frame by Frame. Thank you so much for being here.

SUMMER KAPLAN 00:01:37 Thanks, Chris. I’m glad to be here.

CHRIS ST. JOHN 00:01:41 To set the stage and get things kicked off, your 2015 study questioned the use of gonadal shielding in pediatric radiology. Can you walk us through what led to that research and what you found?

SUMMER KAPLAN 00:01:56 That was a project I did pretty early in my career. My interest goes way back in medical physics and how we acquire the images we acquire. As a resident, I got interested in shielding by chance, just reviewing ACR practice guidelines around X-ray, and there wasn’t strong advice about whether shielding was good or not. I wondered, why don’t we know? Discussing it with our physicists and some of my attending faculty at the time, we started to think about the shields and how they interact with the X-ray equipment.

Shields were implemented a long, long time ago in the 1950s. We started shielding in X-ray, and at that time, imaging techniques were much simpler. X-ray techniques developed in tandem with photography techniques—you can think about it that way. Think about how old-fashioned cameras worked: you have to adjust your light meters, your aperture, and all these complicated things to take a picture, and X-ray machines worked very similarly. Over time, as technology advanced, if you take a picture with a camera now, you just click a button or push a screen, and all the light adjustment is done for you by the camera. X-ray techniques developed similar ways to adjust the amount of light, or radiation, coming in. Our current X-ray technology adjusts the amount of radiation that comes in based on a sensor in the X-ray imaging receptor. When you use a shield, that shield can block the sensor that senses how much light is coming in. It occurred to us that gonadal shielding started so long ago when techniques were much different, and now that techniques have changed, it may not make sense to do that anymore.

CHRIS ST. JOHN 00:03:57 If you were trying to white balance on a home camera, it’s like if you were trying to white balance your camera with a giant black circle in the middle.

SUMMER KAPLAN 00:04:13 The sensor wants to see a certain threshold amount of light or radiation. If you put something in front of that sensor, it doesn’t see that amount of light, so it will actually keep exposing longer until it reaches that threshold. We reasoned that the shields might actually be contributing to higher doses because they could be blocking that sensor in the X-ray machine. That’s what prompted the research we did: the idea that gonadal shields sit right in front of the X-ray sensor and could actually be resulting in more radiation rather than less, which is the opposite of the intention of shielding and protecting from radiation.

CHRIS ST. JOHN 00:04:54 This might sound silly, but are there still machines being used that don’t have these capabilities and where shielding is still appropriate?

SUMMER KAPLAN 00:05:04 There are two ways you might end up with a machine that doesn’t have automatic exposure control. One is if you have a very, very old machine, but that would be decades old, so it’s not as likely. However, when you’re using a portable X-ray technique, you don’t have that same equipment in the imaging receptor plate. Portable X-rays don’t use this dose modulation; it’s based on the technologist setting the technique manually.

For portable X-rays, you wouldn’t necessarily increase dose by using shields. But in that situation, portable X-rays are usually done for the sickest patients who can’t leave their bed. In those cases, the risk is actually higher that you would miss something because a shield is in the way.

The radiation sensitivity of the gonads is actually lower than the bowel, stomach, or bone marrow. If you really want to be protective, you should shield the stomach, not the gonads. If you look at the information we have, nobody is shielding the stomach because you need to see things in that area.

The risks, whether radiation or loss of information from shielding, are not worthwhile. That difference in radiation sensitivity means that if you shield gonads over one of these exposure control devices, you’re going to increase the radiation by quite a bit to organs that are more sensitive. The colon is more sensitive than the gonads. So if you shield the gonads, you’re maybe doubling the dose everywhere else to more sensitive tissues by shielding the gonads, which are less sensitive. It’s really backwards based on what we know now. There’s so much knowledge and information out there that it’s hard to keep everything updated.

CHRIS ST. JOHN 00:07:07 Of course. Your study was in 2015. Have you seen practices shifting and changing since you came out with that?

SUMMER KAPLAN 00:07:15 They really have. The medical physics community really moved it forward. We did the research out of curiosity, but I don’t have the kind of political advocacy or network to make a change like that happen. The medical physics community took that up and helped change policies around the country, because there were a lot of policies in place to promote shielding. At the time those policies were put in place, that was thought to be the right thing to do for patient safety to protect against radiation to the gonads. There were laws throughout the country in almost every state that either required or strongly advised gonadal shielding.

To go against that, we had to work with regulatory bodies to change those statements. Any hospital or radiology practice is going to be reluctant to change before those laws are changed. There is some wiggle room in these laws—shielding is advised unless a physician thinks it isn’t needed—so there is leeway even in existing laws that allows people to stop shielding before laws are changed, because laws take a long time to change. It really spread based on promotion through the medical physics community, and maybe it was a question that had been on people’s minds that people were ready for.

CHRIS ST. JOHN 00:08:42 Was the reason for specifically shielding the gonads versus other body parts always a gonad-specific focus, or were there other sensitive areas or body parts where shielding was common practice?

SUMMER KAPLAN 00:09:00 Historically, the common areas you would see shielded were the gonads, the thyroid—which you still probably see in dental offices or other imaging places—and the breasts, depending on what body part was being imaged. That was initially based on the knowledge we had around radiation risk.

There’s a radiation advisory and research body, the International Commission on Radiological Protection (ICRP), that publishes tables of how radiation sensitive different organs are based on a huge amount of research. They first came out with these numbers in the 1970s, and at that time, our understanding of radiation was much more limited. Based on what we knew then, the gonads, thyroid, and breasts were all considered very radiation-sensitive tissues, so that’s where shielding began.

CHRIS ST. JOHN 00:10:04 What were the results of the study? What did the data say?

SUMMER KAPLAN 00:10:07 Initially, those data were based on research, but also on an abundance of caution, because the last thing you want to do is accidentally deliver high doses of radiation to the gonads and leave someone sterile or risk developing cancer. Specifically, the gonads have reproductive potential, so there was also the risk that you could create mutations passed on to offspring. With other tissues, there’s a risk of cancer or burns elsewhere, but with the gonads specifically, people were concerned about the risk to reproductive capabilities, so they were extra cautious.

Over time, with 50 years of additional data on what radiation does to the gonads, we have not seen any evidence of heritable effects in humans. There is no documentation of radiation to the gonads resulting in mutated offspring, as much as comic books would like to make you think that’s what radiation does. It doesn’t work that way.

CHRIS ST. JOHN 00:11:18 I would love to go in for a CT one day and walk out super powered.

SUMMER KAPLAN 00:11:24 Become The Incredible Hulk all of a sudden!

CHRIS ST. JOHN 00:11:25 Exactly. I could deal with a little bit of extra irradiated strength. Is the practice of gonadal shielding largely put to bed, or are there scenarios where it’s still recommended?

SUMMER KAPLAN 00:11:42 It takes a long time to change practice, especially in a country as big as the United States, where there are so many different practice types and states. For things to percolate through the whole field takes almost a whole generation.

It really starts with training. Technologist training programs are no longer teaching shielding, and that’s where the core change begins. The technologists are the ones responsible for placing the shields, and the more they understand that this is not actually keeping patients safe—that it’s maybe more harmful than safe—the more the field will eventually shift to no shielding. But we read X-rays from outside hospitals all the time, and I still see shields coming from smaller hospitals.

CHRIS ST. JOHN 00:12:40 What would you say to a patient who is used to shielding, goes to a facility with one of these newer machines, and is concerned about not having a shield?

SUMMER KAPLAN 00:12:53 That’s a real challenge, and the people who do that explanation typically are the technologists, so having talking points for them is important.

The key talking points are that we’ve updated our knowledge: not only are the machines different now, but our understanding of risk is different. Initially, we thought the gonads would bear a quarter of the risk in a whole-body radiation event. With more data, we know that only about 8% of the risk is at the gonads. There are risks elsewhere in the body—in the bowel, esophagus, breast tissue, and bones—so the gonads are not as sensitive as we thought.

What I would tell a patient is that our technology has changed, our understanding of risk to the gonads has changed, and it turns out that when you combine shielding with X-rays now, it can actually result in an increased dose because of the newer technology. We don’t want to increase dose unnecessarily, and shielding can also block findings radiologists need to see. So there are several reasons not to use it.

CHRIS ST. JOHN 00:14:16 We’ve touched on shielding patients, but I am naturally curious about staff shielding protocols as well.

SUMMER KAPLAN 00:14:27 That’s a great question, and we get that question a lot, especially from families. Their child is in the X-ray machine with no shielding, while the parents and staff are wearing lead, and the parents ask why their child is left unprotected when everyone else in the room is protected.

There are several reasons for that. The child is there to benefit from the exam, so they are receiving benefit from the radiation. The parents are not receiving any benefit. State laws regulate lead shielding for people who are not there to receive a medical procedure, so we are required by law to provide shielding for non-patients and non-medical personnel in the room. That can mean wearing lead aprons, which is most common, or standing behind a lead glass plate. That is required because parents don’t benefit from any radiation they might receive, whereas the child is benefiting from the exam.

For staff, it’s slightly different because they are working around radiation every day. Their exposure levels are much higher than a patient who comes in for a scan. Staff are in a radiation field every day, so they wear lead to protect themselves. They also wear dosimetry badges because there are annual limits on the radiation a worker can receive, and staff have to make sure they don’t exceed those levels.

CHRIS ST. JOHN 00:16:08 Getting imaged is something everyone will run into at some point in their life. I was talking to a friend last night who is a nurse, and he was talking about all the CTs he’s ordering. There was a study that came out recently, and we were talking about CTs in general. He was commenting on the increase in fear around imaging. I can’t even imagine being a parent, especially with stories coming out like that, going into a room where everyone is wearing all that protective gear.

SUMMER KAPLAN 00:16:55 Exactly.

CHRIS ST. JOHN 00:16:58 You’ve pretty much covered it already, but is there anything else you would add when talking to a family in these situations?

SUMMER KAPLAN 00:17:05 For children, we use extremely low levels of radiation. The amount of radiation used for a patient is relative to their body size, so a one-month-old infant gets a tiny fraction of the radiation an adult would get for the same exam because they’re so small.

Diagnostic imaging uses extremely low levels of radiation compared to therapeutic radiation in oncology or interventional procedures where you’re repairing vessels. Diagnostic imaging, which is what most people encounter, uses very low radiation, even for CT. A CT is generally 10 to 100 times more radiation than an X-ray, and even those levels are relatively low.

We think of it as a risk-benefit ratio. When you’re getting an imaging exam, you should be getting benefit from that exam. That’s the other side of these discussions about radiation and how dangerous it is: there is also a lot of benefit to it, and that’s why we use it.

CHRIS ST. JOHN 00:18:13 That’s where I was about to go with it, too. Yes, there is some quantifiable level of risk associated with it, but compared to the risk of not finding out the problem that brought them in for that X-ray or CT—

SUMMER KAPLAN 00:18:29 Exactly.

SUMMER KAPLAN 00:18:35 When you think about prediction models that say 100,000 people will die of cancer from a certain number of CT scans, those same 100,000 people didn’t die of an aneurysm or a renal infection or the things CT prevents you from dying from because we catch them.

CHRIS ST. JOHN 00:18:52 I was just talking with Dr. Samei at Duke about this on an episode, and what I said to him was, if it means I get to live to see myself get cancer at 60, I’m probably going to get imaged.

SUMMER KAPLAN 00:19:09 That part of the story gets overlooked because it’s sensational. Radiation is invisible and scary—it sneaks up on you—so people like these sensational stories. But there’s the other side to the story, which is that imaging is very helpful.

CHRIS ST. JOHN 00:19:29 In terms of the journey of shielding throughout the country, I know you were saying it’s a slow regulatory process and guidelines change slowly. Where are you seeing this breakdown? Is it larger facilities versus smaller, or more urban versus rural, or is it different by state?

SUMMER KAPLAN 00:19:51 I don’t have a lot of personal experience with that kind of variety, but where I have seen it move forward most quickly and effectively is where there’s an advocate for it. It could be a large hospital system that has a champion who wants to put the work in to change policies, but it could also be a small hospital. It’s really person-dependent at this point, until training changes and people understand not to use it. It could take 10 years for it to completely go away—unless companies stop selling the shields, which might help.

CHRIS ST. JOHN 00:20:29 In terms of legislation, is there a big difference between pediatrics and adults?

SUMMER KAPLAN 00:20:34 No, the legislation is not specific to children or adults. A lot of the research has been done in children, mainly because people are most concerned about shielding the gonads in children due to lifelong reproductive capabilities. In practice, there isn’t much difference in policies, nor should there be.

CHRIS ST. JOHN 00:20:54 Do you have any other points on peds specifically that you’d like to get into?

SUMMER KAPLAN 00:20:58 In pediatrics, the parents or guardians are there looking out for the child, so there’s a lot more concern. Whereas with an adult, part of becoming an adult is just giving into things you don’t understand, so adults will just get the exam, even if they are anxious about it.

There are higher risks associated with radiation use in children because the dangers of radiation stem from its effects on dividing cells. That’s why the gut and bone marrow are highly sensitive: there’s a lot of dividing cells and replacement of gut lining flaking off. Children are growing and have lots of dividing cells, which is one reason we’re more cautious with radiation in children. They also have a longer lifespan during which to develop radiation-induced cancers.

When it comes to gonadal shielding, it’s really about the concern on the part of the family in terms of what this means for the child. Everyone there wants to keep the child safe—that’s the goal of the parents, the staff, and everyone involved—and we just need to understand how best to do that.

CHRIS ST. JOHN 00:22:25 Slightly tangenting, do you have advice for listeners of this show or anyone working in radiology departments who are still using outdated shielding practices? What steps could they take?

SUMMER KAPLAN 00:22:37 There’s plenty of evidence through research and policy that gonadal shielding is no longer recommended. That position comes from professional organizations like the American Association of Physicists in Medicine (AAPM) and the American College of Radiology (ACR), as well as national advisory bodies like the National Council on Radiation Protection and Measurements (NCRP), and the FDA. The FDA no longer recommends shielding, and X-ray technologist societies have also come out against shielding.

If anyone is unsure about whether they can stop, the evidence and policy back stopping it. The difficult thing in practice is communicating that to patients and families. The NCRP has guidelines on how to communicate and flyers written for patient understanding, which are a good resource to help train technologists on how to have these conversations.

CHRIS ST. JOHN 00:23:57 I’ve seen some of the numbers. I know how busy imaging departments are these days and how understaffed they are. There is an infinite amount of work to do and an infinite amount of information to keep up with—technology is getting better every day and there are new regulations constantly.

SUMMER KAPLAN 00:24:18 It really is a lot.

CHRIS ST. JOHN 00:24:21 Speaking of technology improving, are there other emerging technologies or protocols that you interact with regularly that could further reduce radiation exposure, especially in pediatrics?

SUMMER KAPLAN 00:24:34 Definitely. There are a couple of ways to think about it. One is in how we acquire images: pretty much every vendor who sells imaging equipment improves photon capture and imaging technology with each new machine. For hospitals that can afford it, keeping machines updated is a great way to reduce radiation. Detectors are more sensitive and image reconstruction algorithms are much better with each generation. That’s the most expensive and effective way to improve image quality and decrease radiation.

The other area I am very interested in is selecting who needs to get radiation exams. That’s where predictive AI and machine learning tools can help us better understand who benefits from imaging. It’s always said that the lowest radiation study is the one you don’t do. Avoiding studies that don’t provide benefit is good for the patient and good for healthcare economics. Predicting who would benefit most from imaging would be fantastic, though I think that’s still a long way off.

CHRIS ST. JOHN 00:25:56 That’s so interesting. At Imalogix, we’re using machine learning to help with things like patient centering. But you’re talking about using AI to input bodily markers and predict whether a person should get imaged.

SUMMER KAPLAN 00:26:22 You’re never going to have a machine that gives a simple yes or no on whether someone should be imaged, but rather the likelihood—such as the probability of appendicitis based on symptoms and history. That is what doctors do anyway: we take all the information and determine a probability of what is going on. There is so much information, not just in research literature but in patient charts, that it’s hard to take everything into account. Having tools that pull all of that together would be fantastic.

CHRIS ST. JOHN 00:26:55 Are there specific biomarkers or data these theoretical AIs would look at when determining if someone should be imaged?

SUMMER KAPLAN 00:27:10 It’s all probabilities and statistics. You would look at the features the patient presents with: fever, chest pain, shortness of breath. You are more likely to have pneumonia than a knee infection, for example. That’s an obvious example of taking information to make a prediction, but the more information you have, the better you can predict. Using more data from patient charts to help us understand where imaging provides the most benefit would be very interesting.

CHRIS ST. JOHN 00:27:41 It’s very Star Trek, where you do a full-body scan and it tells you what to worry about.

SUMMER KAPLAN 00:27:48 People think they want to know what’s in their body, but there are a lot of things going on in there that you don’t necessarily want to know.

CHRIS ST. JOHN 00:27:56 When all the DNA testing labs were popping up all over the internet, I felt the same way: I don’t want to know.

SUMMER KAPLAN 00:28:05 Radiation risk is very person-specific, just like a lot of disease. Going on a complete tangent, during the COVID-19 pandemic, we saw that it affected people so differently—some people had it without knowing, while others died. Every human is built differently, and it’s hard to predict how something will affect someone. With radiation, it’s the same way: some people might be very sensitive to DNA breaks caused by radiation, and others might not be, but we don’t have a way to know that yet.

For people getting imaging for themselves or their children, I hope they understand that the primary job of medical staff is to keep patients safe, and we would never recommend something we know to be harmful. Changing gonadal shielding practices can seem scary if you are used to shielding, but our knowledge has updated, so we are updating our practices.

The levels of radiation and risk in diagnostic imaging are so low that being shielded a month ago doesn’t mean you or your child were harmed. Doing away with shielding is simply following the ALARA (As Low As Reasonably Achievable) principle in radiology. Because there is a long time between exposure and potential effects, we don’t have a direct cause-and-effect understanding, but the risks are extremely low. Not shielding moving forward just reflects our updated knowledge.

CHRIS ST. JOHN 00:30:19 There are so many things in daily life where you learn, adapt, and change your habits. I was going to bring up seat belts, but that’s a terrible counter-example in this context!

SUMMER KAPLAN 00:30:34 There are all kinds of crazy things we used to do in medicine—like doctors writing prescriptions for cocaine because it was thought to help, and now we don’t do that anymore.

CHRIS ST. JOHN 00:30:43 I used to live in New Orleans, which has a pharmacy museum. There’s a section of heroin, cocaine, and opium prescribed with doctors’ labels, and my favorite was a pack of cigarettes labeled for asthma.

SUMMER KAPLAN 00:31:03 That’s wild! We have to update our knowledge and not just keep doing what we’ve always done.

CHRIS ST. JOHN 00:31:10 The status quo is not necessarily best practice.

SUMMER KAPLAN 00:31:16 It should always be updated.

CHRIS ST. JOHN 00:31:16 Dr. Kaplan, thank you so much for joining us today on Frame by Frame. I really appreciate you being here.

SUMMER KAPLAN 00:31:23 Thank you, it’s been great. Thanks for the conversation, and I hope this is helpful for people.

CHRIS ST. JOHN 00:32:28 Thank you for helping get the word out, too.

Questions from This Episode

Why would a lead shield increase radiation dose instead of reducing it?
Modern X-ray machines use automatic exposure control, a sensor in the imaging receptor that measures incoming radiation and stops the exposure once it reaches a set threshold. A gonadal shield placed over that sensor blocks it, so the machine keeps exposing longer to reach its threshold. The extra exposure lands on surrounding tissue, which raises overall dose.
Is it dangerous that children are no longer shielded while parents and staff still wear lead?
No. The child is there to benefit from the exam, so the radiation serves a purpose for them, while parents receive no medical benefit and are shielded by law as non-patients. Staff work in a radiation field every day and wear lead plus dosimetry badges to stay under annual exposure limits. Pediatric diagnostic doses are also scaled to body size and are very low.
If my child was shielded during a past exam, were they harmed?
No. Diagnostic imaging uses extremely low levels of radiation, and dropping shielding follows the ALARA principle of keeping dose as low as reasonably achievable. A past shielded exam does not mean harm occurred. It only means the evidence has been updated and current practice reflects what we now know.